1. Field of the Invention
The present invention relates to pipe nipples and, more particularly, to pipe nipples used in fluid heating, fluid cooling, and fluid ventilation systems.
2. Description of the Prior Art
Pipe nipples are commonly used to connect two or more pipe segments to one another. In water heating systems, metal pipe nipples can be lined with non-corrosive materials to help retard electrolytic corrosion caused by the metal pipe nipple's exposure to water and oxygen. For example, U.S. Pat. No. 3,093,161 to Jacobson discloses a lined pipe nipple for use in hot water heating systems. The pipe nipple includes a metal body with a plastic insert. The insert prevents the metal body from being exposed to water and eventually corroding. Such an arrangement is expensive to manufacture because two separate components, the metal body and the plastic insert, must be manufactured and then attached to each other. Moreover, expansion and contraction of the separate components increases the potential for water to penetrate between the metal body and the plastic insert, thus reducing the electrolytic corrosion protection.
While plastic inserts may help protect the interior of a pipe nipple from electrolytic corrosion, the plastic inserts do not protect the pipe nipple or the attached piping from galvanic corrosion. Galvanic corrosion can occur when different metals are connected together. In the case of water heating systems, the metal used to construct the water supply pipe and the water return pipe is often different than the metal used to construct the water heater's inlet pipe, outlet pipe, and holding tank. Therefore, the possibility of galvanic corrosion exists.
A non-metallic, electrically non-conductive material can be used to overcome electrolytic and galvanic corrosion. For example, U.S. Pat. No. 4,345,785 to Bradford discloses a polytetrafluoroethylene annular washer positioned between two pipes made of dissimilar metals. The polytetrafluoroethylene washer, commercially sold under the trademark TEFLON, physically separates the pipes, thereby eliminating galvanic corrosion.
In water heating systems, however, another function of the water supply pipe or the water return pipe is to provide an electrical ground for the water heater. If plastic pipe nipples are used to connect a water supply pipe and a water return pipe to a water heater's inlet pipe and outlet pipe, respectively, the electrical grounds between the water heater and the water supply pipe and the water heater and the water return pipe are interrupted.
Therefore, it is an object of the present invention to provide a pipe nipple that can be used in fluid heating systems, fluid cooling systems, and fluid ventilation systems, such as HVAC, which is inexpensive to manufacture.